Refractory furnace tank walls

ABSTRACT

A tank for containing a bath of molten metal in a float glass furnace has a wall formed by a plurality of juxtapositioned prefabricated refractory members. The joints between the members define interstices. Interstices are also being defined adjacent other faces of the blocks. Powdered carbon, alumina, chromium oxide, a carbide or nitride not wettable by molten metal at least partially fills these interstices to prevent the flow of molten metal therein so as to prevent raising of the blocks from their assembled positions by the flow of molten metal behind the blocks. These are in the interstices between the particles of the powder flow paths having restricted cross-sectional areas. The object of these restricted areas and the surface properties of the powder material is to prevent penetration by molten metal.

United States Patent [1 1 Brichard et al.

[ 1 Oct. 23, 1973 REFRACTORY FURNACE TANK WALLS Inventors: EdgardBrichard, Jumet; Joseph Declaye; Jean Autequitte, both ofMoustier/S/Sambre, all of Belgium Related U.S. Application DataContinuation-impart of Ser. No. 872,151, Oct. 29, 1969, abandoned.

Assignee:

Foreign Application Priority Data Oct. 30, 1968 Luxembourg 57,194

US. Cl 65/182 R, 65/347, 65/374 Int. Cl C03b 18/00 Field of Search65/182 R, 99 A, 346,

References Cited UNITED STATES PATENTS 5/1970 Bacchiega et al 266/43 X3,584,475 6/l97l Galey et al 65/374 X Primary ExaminerArthur D. KelloggAttorney-Edmund M. Jaskiewicz [57] ABSTRACT A tank for containing a bathof molten metal in a float glass furnace has a wall formed by aplurality of juxtapositioned prefabricated refractory members. Thejoints between the members define interstices. Interstices are alsobeing defined adjacent other faces of the blocks. Powdered carbon,alumina, chromium oxide, a carbide or nitride not wettable by moltenmetal at least partially fills these interstices to prevent the flow ofmolten metal therein so as to prevent raising of the blocks from theirassembled positions by the flow of molten metal behind the blocks. Theseare in the interstices between the particles of the powder flow pathshaving restricted cross-sectional areas. The object of these restrictedareas and the surface properties of the powder material is to preventpenetration by molten metal.

9 Claims, 10 Drawing Figures PAIENIEflumzs ms- 3761.375

SHEETlUF3 V V i Fig.1.

AN AUTEQUITTE ATTORBzY PAIENIEDUUZMBH' 3.767.375

SHEET 2 OF 3 INVENTORS EDGARD BRICHARD JOSEPH DECLAYE JEAN AUTEQ UITTEPATENIEBIIBI 23 ms 3.767; 375

SHEET 3 [IF 3 INVENTORS EDGARD BRICHARD JOSEPH DECL JEAN AUTEQ E ATTOREY 1 REFRACTORY FURNACE TANK WALLS RELATED APPLICATION This applicationis a continuation-in-part of the copending application filed by thesame-named applicants on Oct. 29, 1969 and having Ser. No. 872,151 nowabandoned.

The present invention relates to refractory float glass furnaces of thetype having a tank therein for containing a bath of molten metal, moreparticularly, to the construction of the refractory wall in order toprevent molten metal from penetrating behind refractory blocksconstituting the wall.

Refractory walls for furnaces are generally formed by justzpositioning aplurality of prefabricated refractory members or blocks. When this wallis employed to support a bath of molten liquid some consideration mustbe given to sealing the joints between these refractory members againstthe flow of'the bath liquid. Such refractory walls have been made fluidtight merely by relying on the solidification of the molten liquid inthe joints. However, this arrangement is not particularly effectiveespecially where the temperature of the bath liquid is considerablyabove its melting point. Under these circumstances the bath liquid willsolidify only at a considerably great distance from the interior face ofthe furnace wall so that the bath liquid is still able to penetrate aconsiderable distance into the wall. This penetration of the bath liquidinto the wall is disadvantageous since there will be some bath liquidstationary in the wall joints. The liquid will bring about corrosion ofthe wall, the liquid will become polluted by the products of suchcorrosion, and the fioor blocks may be lifted when their density is lessthan that of the bath liquid and this liquid is'able to flow behind theblock through a joint opening to the liquid bath. It is particularlyimportant to prevent the penetration of the molten bath liquid throughthe refractory wall so that the liquid does not come in contact with themetallic elements positioned behind the refractory blocks. The strongcorrosive action of the molten material on these metallic elements canbe extremely destructive. It is therefore desirable to position someform of a barrier within the refractory wall to prevent the passage ofthe bath liquid through the wall. The position of the barrier may dependto a large extent upon the thickness of the furnace wall.

It is therefore the principal object of the present invention to providea novel and improved refractory wall for a tank furnace containing abath of molten metal.

It is another object of the present invention to provide simple andeffective fluid tight joints between and behind the refractory membersforming a furnace wall.

It is a further object of the present invention to provide a refractorywall of refractory blocks for supporting a liquid bath with restrictedjoints pervious to gas but tight to the liquid bath.

According to one aspect of the present invention a refractory furnacetank containing a bath of molten material such as molten tin may have awall comprising a layer of justaposed prefabricated refractory members.This layer of refractory members is positioned on the interior surfaceof the tank wall and defines a thickness portion of the furnace wall.The joints between interior faces of the refractory members define flowpaths extending from the interior of the furnace tank through at least aportion of the wall thickness. Means are provided in these paths forpreventing the flow of bath liquid therethrough. These means may bepositioned in at least portions of the joints so as to modify the crosssectional area of a flow path. The means form restricted cross sectionpaths which also have surface properties which prevent the penetrationof bath liquid along these paths through at least a portion of the wallthickness either in the joints between the members or elsewhere. Thejoints may be formed by various configurations of the opposing faces ofadjacent refractory blocks or merely closely positioning these faces toeach other. There may be disposed in the joints a loosely packed porousmass of material whose surface properties prevent the penetration of thebath liquid. The materials within the joints of this layer of refractorymaterials and the configurations and dimensions of these joints aredetermined so as to prevent the penetration of at least a portion of thewall thickness by the bath liquid.

Preventing of the raising or lifting of the refractory blocks from theirassembled positions is thus obtained according to the present inventionby providing a barrier of pulverulent material which is not wettable bythe molten metal and which is situated under the blocks or the samebarrier situated under or below the periphery of the only face of theblock which is directed to the interior of the tank.

The present invention can eliminate or at least significantly reduce theamount of bath liquid which has solidified in the joints of therefractory wall after the operation of the furnace has been stopped.This solidified liquid represents an economic loss since it is not beingused in the operation of the furnace and at the same time presentspossible sources of corrosion of the wall members. By providing thepresence of this liquid in the refractory walls the pollution of thebath liquid by dissolved or suspended bodies is significantly reducedand vitreous phases and gases which may result'from contact of the bathliquid and certain constituent materials of the refractory wall may beavoided or reduced.

It is known to construct a tank for retaining molten aluminium having arefractory wall comprising a plurality of refractory blocks with loosesilicon carbide poured between the blocks. According to the presentinvention the interstices between fabricated refractory blocks forming awall of the furnace tank arefilled with a pulverulent material, which ischaracterized by not being wettable by the molten metal, i.e., tin, inthe furnace and the density of the pulverulent material is less thanthat of the molten tin. i

The non-wettability of the carbon prevents the-molten tin frompenetrating the interstices and, in effect, isolates the granules ofcarbon so that as a result these carbon grains do not have any tendencyto rise to the surface of the molten bath. The density of the carbonmaterial between the refractory blocks ranges from 1.8 to 2.1 which isconsiderably less than the density of molten tin which is about 7.3.This relationship is contrary to that in known prior art where thedensity of this silicon carbide powder is greater than that of themolten aluminium in a furnace.

The use of a compacted material with a binder as disclosed in knownprior art has the disadvantage that this compacted mass will crackbecause of any movements of the blocks of the refractory wall. Thepresence of such cracks will eventually become enlarged will per-' mitthe molten metal to penetrate between the blocks and produce either alifting of the blocks or a corrosion of the supporting structure for theblocks. A loosely packed pulverulent material in the joints between andadjacent the blocks has the advantage that the particles are able toslide over each other in the event of any movement of the blocks but thenonwettability of the particles will still prevent penetration by themolten metal.

Other objects and advantages of the present invention will be apparentfrom the accompanying description when taken in conjunction with thefollowing drawings, which are exemplary, wherein;

FIG. 1 is a transverse vertical sectional view of a portion of a furnacewall which forms a tank for molten material according to a form of thepresent invention;

FIG. 2 is a transverse sectional view of a portion of a refractoryfurnace wall showing a modification thereof;

FIGS. 3-7 are similar to FIG. 2 and show further modifications accordingto a form of the present invention;

FIGS. 8 and 9 are top plan views of modifications in furnace wallsaccording to a form of the present invention; and

FIG. 10 is a top plan view of another form of refractory furnace wallaccording to the present invention.

Proceeding next to the drawings wherein like reference symbols indicatethe same parts throughout the various views a specific embodiment andmodifications of the present invention will be described in detail.

As may be seen in FIG. 1 a refractory furnace tank incorporating thepresent invention has a floor and a side wall 22 which are both formedof layers 24, 26 and 28. The layer 24, which is toward the interior ofthe furnace, is comprised of a plurality of slabs 30 with each slabcomprising a body 31 of silico-argillic refractory, ceramic or ofsilicon carbide. Each body portion 31 has on its face 32 which isdirected toward the interior of the furnace and on the four adjacentside faces 34 a compact coating 36 of carbon. The carbon coating is madeadherent by means ofa binder of refractory cement. Adjacent facesbetween the slabs 30 define joints 38 which are not filled but which arefluid tight. Where the carbon coating 36 on the side faces is notaccurate it may be necessary to trim this coating by a planing operationto insure that the joints 38 are sufficiently narrow. The joints 38 willbe sufficiently tight with respect to the molten tin bath up to theoperating temperatures of about 1,000C when the space in the jointranges up to about 2mm. Up to this width the surface and interfacialtensions at the interfaces between the molten tin, carbon and gasespresent in the joints will prevent penetration of the liquid.

Where there is a possibility of the space in the joints 38 exceeding 2mm. even in localized areas it may be preferred to subject the layer 24to compression in one direction or even in both directions when viewingth layer in plan. Such compression may be obtained by means ofadjustable clamps 40 which exert compressive forces against two verticaluprights 42 against cross-members 44 positioned against outer wall 46 ofthe furnace at the level of the layer 24. The tops of the uprights 42are connected and may also be used for the construction of a known typeof furnace crown which is not shown in the drawing.

The layer 24 contacts against layer 26 which is formed ofsilico-argillic blocks 50 which are shown in the art and are usedparticularly because of their thermal insulating properties. This layer26 rests upon an outer wall or shell 28 of steel plate. The supportframework for the furnace is not shown in the drawings for purpose ofclarity. With this construction it is not necessary to provide anyexpensive or complicated anchoring structure for the ceramic blockssince the molten tin is unable to penetrate below the lower face of theblocks 50 and thus is not able to lift these blocks. When the bathliquid is a good conductor of heat or electricity it is particularlydesirable to prevent this liquid from penetrating into the wall sincepreventing this penetration would reduce energy losses and the need totake any remedial measures.

According to the present invention the members constituting the layermay consist primarily of carbon at least along their surfaces formingjoints with other members. The member may consist entirely of carbon orthe carbon may be only at these joint surfaces. It is to be understoodthat carbonincludes graphite as well as amorphous carbon which may havesuitable additives as well as certain impurities. Carbon is preferredsince it is not wetted by the molten metals such as tins, used in theliquid bath or by various glasses.

When forming a layer of blocks it is preferable to use blocks ofrelatively large dimensions so as to limit the number of joints. A blockaccording to the present invention also includes relatively large thinmembers which might better be described as slabs. The use of blocks ofrelatively large dimensions has the further advantage that the merepenetration, e.g., fortuitous, of liquid a short distance beneath itslateral edges will not cause the block to lift as quickly as would bethe case when its dimensions are smaller.

By fitting the blocks 30 tightly together as described above the spacesin the joints will be so small that the bath liquid will not be able topenetrate between the joint surfaces. This arrangement is particularlyadvantageous where there are rapidly flowing currents of liquid whichcould entrain granular materials from the joints. Clamping of the blocksagainst each other by subjecting them to compressive forces which'areadjustable enables the width of the joints to be limited in spite of thethermal expansion due to fluctuations in furnace temperatures. Suchvariations are particularly likely to occur when the furnace is firstbeing started up.

In FIG. 2 a powdered carbon 54 which is impermeable to molten tin isfilled in the joints between the refractory blocks. The carbon grainsare smaller than 1 mm. and preferably smaller than 0.1 mm. Therefractory layer adjacent the interior of the surface comprises aplurality of slabs 56 of graphite with their joints 58 being filled withthe powdered carbon 54. The slabs 56 are positioned on a relativelythick layer of powdered carbon 60 in which are embedded metallic tubes62 through which may flow a thermal conditioning medium. Depending onthe regions of the furnace floor these tubes may be used for heating orcooling with the thermal effect being achieved by means of water, coldair, hot air circulating as indicated by the arrows 63 or by the use ofelectrical resistors which are not shown in the drawing. Heat is readilytransmitted from the liquid positioned on the slabs 56 to the thermalelement or vice versa because of the good thermal conductivity of thepowdered carbon 54 and the graphite slabs 56. The layers 26 and 28 aresubstantially the same as the corresponding layers described in FIG. 1.

Analogous results have been found with powders of A1 Cr O carbides andnitrides not wettable by molten tin in the same conditions as carbonpowder in the application according to FIG. 2 as in other applicationswher powder is used.

In FIG. 3, there are formed joints 64 between slabs 66 of silicoargillicceramic. Each joint 64 is formed by a projection 68 on a face 70 of oneblock positioned within a groove 72 on the adjacent face 74 of the nextcontinguous block. The projection and groove have a sinuousconfiguration so that an inter-locking effect is achieved. The blocksrest upon a bottom bed 76 of powdered carbon. The joints 64 are alsofilled with powdered carbon and these joints together with the bottombed 76 have a thickness ranging from 2-10mm.

In FIG. 4, a refractory insulating concrete 78 has been cast on theshell 28 so as to form a foundation surface with the top face of thissurface having grooves 80 intersecting at right angles. Rectangularslabs 82 of graphite each have a recess 84 in their bottom face so as todefine a downwardly projecting peripheral rib 86 on the slab bottomface. The peripheral ribs 86 of two adjacent slabs are seated togetherin a groove 80. The joints 88 between adjacent slabs are open and have awidth of about 6mm. so that molten tin is able to penetrate into thisjoint. The molten tin, however, is stopped at the level of the ribs 86by a carbon layer 90 which is positioned on the foundation layer andwithin the grooves 80. In certain cases grains from the carbon layer 90may be entrained within the molten tin and flow upwardly through thejoint 88 to float upon the tin, however, these would not float upwardlyabove the horizontal plane defined by the bottom faces 92 of the ribs86. lnfact, the grains located above this plane cannot be entrainedsince they have a tendency to rise. In this manner, the major portion ofeach of the slabs 82 is protected against erosion of the subjacent layerwith the result that raising of a slab is impossible. This measure is anadditional precaution since the carbon powder located beneath the joint88 is already extremely well protected from erosion because of itsdistance from the liquid mass of molten tin. The liquid-tight layer 90is separated from the liquid bath by a layer of spaced blocks 82. Incertain instances, a series of metallic plates, such as tungsten, may beplaced on this liquid-tight floor of the blocks 82. These metal platesare not welded but are merely positioned-on the slabs, and are not shownin the drawings. It is also possible to provide a second layer ofrefractory slabspositioned on the layer of slabs 82 shown in thedrawing. The second layer of slabs could have a greater density thanthat of the molten bath.

In the wall structure shown in FIG. there is provided a layer ofgraphite slabs 94 with the adjacent edges of successive slabs having aconfiguration to form a joint 96 having a pair of reverse bends therein.The

joint is provided with a region 98 which is located higher and furtheralong the path of the joint as measured from the interior of the furnacethan the region 100 which is lower and closer to the interior of thefurnace. Thus if any grains of the carbon powder within the joint 96were accidentally to escape toward the surface of the bath, such erosionof the joint would be arrested immediately after the lower region 100.The

graphite slabs 94 form a joint 102 between their rear faces and a layerof blocks 50 of silico-argillic ceramic. No material is interposedwithin the joint 102. In order to facilitate inserting of the powderedcarbon in the joint 96 the powder may be tempered with the minimumquantity of water necessary to obtain a mortar having a consistencycapable of being retained by adhesion on the ridge and groove definingthe joint 96. This water is obviously rapidly eliminated by drying sothat in operation the joint 96 if filled with loose powdered carbon.

Any gases which are evolved are able to escape through the pores of thejoints. Since the escape of such gas bubbles into the bath of molten tinand particularly below the glass ribbon are disadvantageous, a suctionmay be provided with an aperture 103 connected by a conduit 104 to apump which is not shown in the drawing. In order to collect the glassfrom as wide an area as possible an oblique cut-out 105 is formed in thecorners of the blocks 150. An angle from 106 is positioned in thecut-out 105 and is welded at a number of points to the plate or shell28. Since the quantity of the gases which are to be exhausted isrelatively small these gases can readily circulate in the joints 96, 102and 108 and infiltrate between the angle iron 106 and the plate 28. Thesuction through the conduit 104 is established during the starting ofthe furnace but after a period of operation the evacuation of thesegases can generally be discontinued.

The furnace wall structure shown in FIG. 6 combines the advantages ofthe joints shown in FIGS. 3 and 5. A joint 110 is formed betweensuccessive slabs 112 and 113 and has a lower region 100 or first zoneand a high region 98 or second zone as in FIG. 5. However, the lowerportion 114 of the joint is inclined to the vertical toward thelift-hand slab 112 as viewed in FIG. 6 so that a projecting portion 115on the slab 1 12 is not only between the regions 1 l6 and 118 of theadjacent slab 113 which are located on the same horizontal plane butalso between regions 120 and 122 of the same slab 113 located on avertical plane which is perpendicular to a surface 124 of the face ofthe layer in contact with the molten tin bath. This arrangement not onlyprovides for inter-locking of adjoining slabs but also a trapping of thepowder in the joint 110 should accidental erosion occur. Preferably, thefaces 126 and 128 forming the projection or tongue 115 define an acuteangle toward the end of the projection in order to facilitate ,thepositioning of the slabs. It is thus not necessary to position the slab113 by moving the slab in a direction perpendicular to the plane of thedrawing but a slab may be introduced in the direction indicated by thearrow .130. This angular insertion of the slab 113 insures the grip ofthe tempered powder for the joint during this opera-j tion.

In FIG. 7, a layer of graphite slabs 132 is positioned on several layersof granular materials having thermal insulating properties considerablysuperior to those of the usual refractory ceramic blocks'50. 0n thesteel shell or wall 28, there are superimposed a layer of highlyinsulating mineral W001 134, a bed of Koalin fibers 136 having 43percent alumina which is more refractory than mineral wool, a layer ofpowdered carbon 138 and finally the graphite slabs 132. The joints 140between adjacent slabs are not filled and these slabs need not bepositioned particularly close together. Fluid sealing is obtained in theupper portion of joint 140 by means of a groove 142 having with inclinedslopes 144. A graphite strip 146 having a trapezoidal shape is insertedwithin groove 142. The faces 144 of the groove 142 and the faces andangles of strip 146 are accurately formed so as to minimize thethickness of the joints 148 between the strip and the groove walls.Should the spacing of joints 140 increase from deformations or othercauses the strips 146 will be depressed under the forces exerted by thebath of molten tin so that the joints 148 will be very close and fluidtight. The layers of loose material used in the joint 107 may be eitherin powder or fiber form.

It is thus apparent that the joints illustrated in FIGS. 2-7 allfunction to stop the flow of bath liquid either between the refractorymembers or along the rear faces of the refractory members formed in alayer adjoining the interior of the furnace. Preventing the bath liquidfrom reaching the rear faces of the blocks eliminates the relativelyexpensive anchoring structures for these blocks. Sealing of the rearfaces of the blocks is also a safety measure where there is anylikelihood of the joints between the blocks opening because ofdeformations due to the effects of heat. Further, the resistance ofthese joints to the penetration of the bath liquid can be significantlyincreased at points positioned further from the liquid bath because ofthe temperature drop in a direction away from the bath. A furtheradvantage of sealing of the joints at the rear faces of the blocks isthat in the case of a floor structure the vertical joint is undergreater stress than the horizontal joint beneath the blocks since in avertical joint the weight of the molten bath tends toward a penetrationof the bath liquid of the joint. Light solid or gaseous particles whichmight arrest this penetration are evacuated much more easily from thevertical joint.

A mutual interlocking of adjoining blocks in the layer decreases thelikelihood of lifting of light blocks since one or more blocks whichmight be susceptible to such a lifting because of a deep penetration ofthe liquid would be retained in position because of the interlockingrelationship. Thus, such blocks which are subjected to a lifting forcewould not be removed from the layer of blocks.

A liquid seal is attained in the spaces between the grains or particlesof a powder filling a joint between slabs. Regardless of the dimensionsof the grains the spaces between the grains are so small that theliquids which do not wet the grains will not penetrate into the spacesbetween them. It has been found that such a liquid seal is highlyreliable and that the grains which are lighter than the liquid are notlifted and floated on the liquid when these grains are not wetted by theliquid. Such non-wettable powders are further advantageous since theycan be subjected to internal movements without losing their tight seal.Such movements may occur when the dimensions between joints variessubstantially because of the action of heat on the adjacent solidrefractory blocks.

By filling the joints between successive blocks with powder it is thusnecessary to provide only the amount of molten materials necessary toform the bath in the furnace. It is not necessary to allow an additionalquantity of liquid for filling the joints as was the previous case. Thequantity of powdered material which must be used to form the liquidtight seal depends on the volume of the spaces between the refractoryblocks in the furnace wall. Under certain circumstances the refractoryblocks may be made of a wettable material and non-wettable material isused in powder form to seal the joints between the blocks. It is alsopossible to cover the wettable material with a film of non-wettablematerial on those faces which are to be used in forming the joints. Thiscan be done in such a way that a liquidtight seal is obtained only inthe presence of a nonwettable material.

In forming the joints according to the present invention at least aportion of the powder in the joints is fixed in position by means ofminimum amount of a binder which thus minimizes any erosion of thejoints even when the joints are defined by plane surfaces of adjoiningblocks. The use of binder also facilitates positioning the powderbetween the blocks particularly in vertical or thin joints. It ispreferred that the binders be rich in carbon so that the binder itselfis not wetted by the liquid contained in the furnace tank. Preferablythe binder should be rich in carbon at least in the upper portion of thejoints which comes into contact with the molten tin bath. This carbon inthe binder will prevent the tin from coming into contact with materialsother than carbon which may be used in forming the joints. Solutionscontaining sugar and heavy hydrocarbons may be used since when they areheated they leave a residue consisting essentially of carbon. Even whena binder is used it is preferred that the powder thus fixed in positionbe porous to insure ready evacuation of any gases which may be evolved.These gases should be evacuated in a direction away from the liquid andtoward the exterior of the furnace. The gases include not only thosewhich might be released during the operation of the furnace but also anygases which may be produced from the setting of the binder either duringthe temperatures encountered during the use of the furnace or during theinitial heating-up of the furnace.

Differential conductivity in longitudinal and transverse directions of afurnace wall may be obtained between the blocks of a tight layer by theforming of the joints between blocks so that the joints in one directionhave a different resistance to heat transmission than the joints inanother direction. This arrangement will significantly limit thetemperature gradient in one direction while producing a strong gradientin a perpendicular direction. Further, cooling or heating effects can beconcentrated in particular areas. The differences in conductivitybetween joints can be readily obtained merely by forming the joints ofvarying thicknesses.

The joints between the blocks are then filled with a.

suitable material which may either be the bath liquid itself if it is aninsulator. Materials of different conductivity may also be used toinsulate joints to obtain such conductivity differentials. For example,the bath liquid may be in some joints and an insulating material may bepositioned in other joints. Depending upon the materials, thisarrangement permits greater flexibility for a wide range of adjustmentof the conductivity differential.

Particular arrangements for obtaining thermal transmission differentialsin the thickness of a layer of carbon slabs are illustrated in FIGS.8-10. In FIGS. 8 and 9, a layer of refractory blocks is formed which isrelatively insulating in a direction indicated by the arrow X but hasgood conductivity in a perpendicular direction as shown by the arrow Y.The joints or 151 in the direction X are formed to be conducting whereasthe joints 152 or 153 in the direction Y are formed to be insulating. Inthe conductive joints 151 the molten metal of the bath itself may beused. In the alternative, a filling of a conductive powder, such ascarbon, with a preferably conductive binder may be used. In theinsulating joints 153, a ceramic powder, such as Kaolin preferablywithout a hinder, or a liquid of the bath itself, if it is insulating,may be used. Joints filled with wettable powder may be made fluid-tightclose to the inner surface of the wall by a local thin application ofpowdered carbon, with a binder if desired, or by reducing the dimensionat that point of the joint between the slabs if they are non-wettable.The difference in conductivity may also be produced from the differencein the thickness from one group of joints 150 to another 152 as may beseen in FIG. 8.

In FIG. it is possible to vary the conductivity along axes other thanstraight lines. A layer of graphite slabs 56 is provided with a hotpoint 158 which can be insulated radially by means of wide circularinsulating joints 160. At the same time circular conduction is enhancedby the relatively narrow joints 162.

Thus it can be seen that the present invention has disclosed in a floatglass furnace the use of powdered carbon in spaces formed along faces ofcarbon blocks constituting a refractory wall of the furnace tank inorder to prevent the flow of molten tin behind the blocks although thedensity of the pulverulent carbon between the refractory blocks isconsiderably less than the density of molten tin. The non-wettability ofthe carbon by the molten in prevents the molten tin from penetratinginterstices between and adjacent the blocks forming the refractory walland from flowing under a block and a substantial portion of the lowerface of the block to prevent lifting of the block. The joints betweenrefractory blocks which are filled with pulverulent material may belinear, sinuous or have some other configuration which would tend torestrict the flow path between or adjacent the blocks. The presence ofthe pulverulent material in linear joints between refractory blocksconstitutes an effective barrier against molten tin. This barrier isachieved by the use of pulverulent material without a binder and thepulverulent material may be loosely packed in the interstices betweenand adjacent the refractory blocks.

It is to be born in mind that the present invention has many otherapplications other than the tank furnaces which contain a molten metalor molten glass as described above. The invention is particularlyapplicable to a furnace as used in the glass industry for treatment ofglass by the float process in which at least a portion of the tankcontaining liquid must be tightly sealed to prevent escape of theliquid. The invention is particularly suitable to a wall which is sealedagainst tin and its alloys or for molten salts retained in a tank formedof carbon slabs. The carbon slabs and the powdered carbon between theslabs possess to a large degree the properties disclosed above accordingto the present invention. Further, the coating of carbon has theadvantage of bettering the convection currents of liquid and ofpreventing adhesion of any molten glass which may come into contact withthe walls of the tank. While the wall structure has been disclosedherein as comprising the floor of a tank it is to be understood thatwalls other than the floor may also incorporate the present invention.

It will be understood that this invention is susceptible to modificationin order to adapt it to different usages and conditions, andaccordingly, it is desired to comprehended such modifications withinthis invention as may fall within the scope of the appended claims.

What is claimed is:

1. In a wall for a refractory furnace tank for making glass floating ona bath of molten metal, the combination of a plurality ofjuxtapositioned prefabricated refractory blocks defining at least athickness portion of a refractory furnace tank wall, there beinginterstices in the joints between the interior faces of said blocks,said interstices being filled with a pulverulent material not wettableby the molten metal and whose density is less than that of the moltenmetal in order to prevent penetration of the metal into the interstices,and wherein said interstices have a sinuous groove configuration so thatan interlocking effect at said joints between the interior faces of theblocks is achieved.

2. In a wall for a refractory furnace tank for making glass floating ona bath of molten metal, the combination of a plurality ofjuxtapositioned prefabricated refractory blocks defining at least athickness portion of a refractory furnace tank wall, there beinginterstices in the joints between the interior faces of said blocks,said interstices being filled with a pulverulent material not wettableby the molten metal and whose density is less than of the molten metalin order to prevent penetration of the metal into the interstices, andwherein said interstices have a configuration to define a higher and alower zone with said higher zone being further from the faces of theblocks toward the interior of the tank than said lower zone, thedistances being measured along the said interstices.

3. In a wall as claimed in claim 1 wherein said pulverulent material isprincipally carbon.

4. In a wall as claimed in claim 1 wherein said interstices are alsolocated along faces being behind the blocks from the interior of therefractory furnace tank.

5. In a wall as claimed in claim 3 wherein the grains of carbon aresmaller than 0.1mm.

6. In a wall as claimed in claim 1 wherein said pulverulent material isloosely packed.

7. In a wall as claimed in claim 1 wherein said blocks have downwardlydirected ribs around at least the major part of their bottom faces,means under said juxtaposed blocks for defining a foundation surfacethereunder, there being recessed means in said foundation layer toreceive said ribs, said pulverulent material being between said blocksand foundation surface, at least along the side faces of said ribs.

8. In a wall as claimed in claim 1 where said juxtapositioned blocksform at least one layer of a wall also comprising means in theinterstices between the blocks for providing different resistances toheat transfer in different areas of the wall.

9. In a wall as claimed in claim 1 wherein said pulverulent material isA1 0 Cr O or carbides and nitrides not wettable by molten tin.

2. In a wall for a refractory furnace tank for making glass floating ona bath of molten metal, the combination of a plurality ofjuxtapositioned prefabricated refractory blocks defining at least athickness portion of a refractory furnace tank wall, there beinginterstices in the joints between the interior faces of said blocks,said interstices being filled with a pulverulent material not wettableby the molten metal and whose density is less than of the molten metalin order to prevent penetration of the metal into the interstices, andwherein said interstices have a configuration to define a higher and alower zone with said higher zone being further from the faces of theblocks toward the interior of the tank than said lower zone, thedistances being measured along the said interstices.
 3. In a wall asclaimed in claim 1 wherein said pulverulent material is principallycarbon.
 4. In a wall as claimed in claim 1 wherein said interstices arealso located along faces being behind the blocks from the interior ofthe refractory furnace tank.
 5. In a wall as claimed in claim 3 whereinthe grains of carbon are smaller than 0.1mm.
 6. In a wall as claimed inclaim 1 wherein said pulverulent material is loosely packed.
 7. In awall as claimed in claim 1 wherein said blocks have downwardly directedribs around at least the major part of their bottom faces, means undersaid juxtaposed blocks for defining a foundation surface thereunder,there being recessed means in said foundation layer to receive saidribs, said pulverulent material being between said blocks and foundationsurface, at least along the inner side faces of said ribs.
 8. In a wallas claimed in claim 1 where said juxtapositioned blocks form at leastone layer of a wall also comprising means in the interstices between theblocks for providing different resistances to heat transfEr in differentareas of the wall.
 9. In a wall as claimed in claim 1 wherein saidpulverulent material is A12O3, Cr2O3, or carbides and nitrides notwettable by molten tin.